1. Field of the Invention
The invention relates to an optical trapping skirt for adjusting the diameter of a beam passing thereof, and more particularly to an optical trapping skirt for eliminating the undesired light, such as reflected light and stray light.
2. Description of the Related Art
FIG. 1 schematically shows a conventional trapping skirt. As shown in FIG. 1, the conventional trapping skirt is also named Wood""s horn, and has a hollow-horn structure 1 painted dark. When a beam b enters the conventional trapping skirt 1, the beam b is trapped and cannot escape. However, the size of the opening 2 of the conventional trapping skirt 1 is fixed. When the cross-sectional area of a beam is greater than the opening of the conventional trapping skirt, the conventional trapping skirt merely captures partial light. Moreover, the conventional trapping skirt cannot capture some light having special shape, such as an annular light.
FIG. 2 schematically shows a conventional diaphragm. As shown in FIG. 2, the conventional iris diaphragm 3 is a two-dimensional plane structure and has a plurality of knife-blades 4 lapping over each other. The conventional iris diaphragm 3 has a pupil 5, whose size is varied and controlled by a manual or automatic mechanism. Consequently, the desired light passes the pupil of the conventional diaphragm, and the undesired light is blocked by the knife-blades. However, when the undesired light is incident on the knife-blades, the reflected light r is generated. When the reflected light r is incident on any optical parts, it is easy to transfer the reflected light r into stray light m. The stray light m is capable of traveling through the conventional diaphragm 3, and the noise to signal ratio is increased.
To solve the above problems, it is an object of the present invention to provide an optical trapping skirt for adjusting the diameter of a beam passing thereof. The invention combines the conventional trapping skirt and the mechanism of the iris diaphragm, so as to block the undesired light entirely.
According to the object mentioned above, the optical trapping skirt for adjusting the diameter of a beam passing thereof includes a body having a first opening, a second opening larger than the first opening, and a sidewall extending from the first opening to the second opening, and an iris diaphragm of bell shape having an aperture which is smaller than the first opening. The iris diaphragm of bell shape is positioned in the sidewall and installed on the second opening, so as to construct a ring like cavity.
One feature of the invention is that when a beam having a diameter greater than the aperture enters the first opening, the undesired light is trapped in the ring like cavity by adjusting the aperture size. Furthermore, the invention can vary the diameter of the beam passing the first opening.
Another feature of the invention is that the undesired light is trapped in the ring like cavity wherefrom the undesired light cannot escape.
Another feature of the invention is that the optical trapping skirt is further has a stand. Thus, the optical trapping skirt is applied to any optical system.
The invention has an advantage of eliminating the stray light and the background light.